It is known to use a sputtering process (sometimes referred to as a physical vapor deposition) to form relatively thin layers in semi-conductor fabrication processes. For example, sputtering is sometimes used to form relatively thin metal diffusion barrier layers and/or anti-reflective layers to cap semi-conductor structures.
A schematic illustration of a conventional sputtering apparatus 100 is shown in FIG. 1. In particular, the sputtering apparatus 100 represents what is commonly referred to as a Hollow Cathode Magnetron (HCM) sputtering apparatus. Referring to FIG. 1, the HCM sputtering apparatus 100 includes a “cupped” target 102 surrounded by electromagnetic coils 106A-106H. Shields 114 extend from the cupped target 102 to a surface 112 holding a substrate 110 on which relatively thin metal layers can be deposited by the sputtering process. It will be understood that the HCM sputtering apparatus 100 is sometimes referred to as “hollow” due to the definition of an inner region 116 by the “cupped” shape of the target 102.
In operation, a vacuum is established in the inner region 116 between the cupped target 102 and the substrate 110. Argon gas is admitted to the region 116, which is ionized by a magnetic and electric field provided thereto. The ionized Argon gas is accelerated toward the cupped target 102, which causes a portion of the material that makes up the cupped target 102 to be ejected outwardly. The ejected portion of the target is directed toward the substrate 110 by fields (electric/magnetic) generated by the electromagnetic coils 106A-H. Accordingly, the material ejected from the cupped target 102 is deposited on the substrate 110. Conventional HCM sputtering apparatuses are further discussed, for example, in U.S. Pat. No. 6,589,398, to Lu et al. entitled Pasting Method for Eliminating Flaking During Nitrite Sputtering, the contents of which are incorporated herein by reference in its entirety.
It is known to use the conventional type of HCM apparatus discussed above to form Titanium Nitride (TiN) layers on substrates using a cupped Titanium (Ti) target using Argon (Ar) and Nitrogen (N2) in the inner region 116. An applied magnetic/electric field is used to accelerate the Argon (Ar) toward the Titanium target 102 thereby causing a portion of the Titanium target to be ejected and accelerated toward the substrate 110. The ejected Titanium combines with the N2 to form a TiN material that is deposited on the substrate 110. It is known to deposit such TiN materials at the bottom of contact holes in the substrate 110 to form, for example, TiN barrier layers to reduce the diffusion of conductive materials (subsequently formed in the contact holes).
In particular, it is known to operate the conventional HCM sputtering apparatus 100 to form TiN layers in one of two modes: Metallic TiN mode or poisoned TiN mode. In Metallic TiN mode the amount of Ti generally exceeds the amount of N2 in the TiN layer using Ar flow rate that is much greater than the flow rate of N2. For example, it is known to sputter Ti using the conventional HCM sputtering apparatus 100 using flow rates of about Ar 135 sccm and N2 28 sccm.
In contrast, in poisoned TiN mode (sometimes referred to as Nitrided TiN), the amount of Ti in the TiN is about equal to the amount of N2 and the Ar flow rate is less than the N2 flow rate. For example, it is known to sputter TiN in poison TiN mode using the conventional HCM sputtering apparatus 100 using an Ar flow rate of about 30 sccm and an N2 flow rate of about 70 sccm (that is using an Ar flow rate that is less than the N2 flow rate). It is known that the poisoned TiN mode sputtering may exhibit superior diffusion barrier layer properties compared to Metallic TiN mode sputtering.
Even with the use of the type of conventional HCM sputtering apparatus 100 discussed above in reference to FIG. 1, it is known that several types of problems may be exhibited with this approach. FIGS. 2-4 illustrate some common problems associated with contact holes formed in substrates of relatively high density integrated circuits. High density contact holes can have relatively high aspect ratios such that the depth of the contact hole is relatively deep compared to the width of the contact hole. It is known that it can be difficult to completely form conductive materials in high aspect ratio contact holes.
For example, FIG. 2 illustrates an insulating layer 205 on a substrate 200 having an impurity doped region 203 formed therein that is exposed by the contact hole. A diffusion barrier layer 207 (such as a TiN diffusion barrier layer) is formed in the contact hole and on the exposed surface of the impurity doped region 203. A conductive layer 209 is formed on the diffusion barrier layer 207 including in the contact hole. According to FIG. 2, because of the high aspect ratio of the contact hole, a void 211 may be formed in the contact hole because of the formation of an overhanging portion 215 that may block further deposition of the conductive layer 209 in the contact hole. The formation of metal layers in contact holes is also discussed, for example, in U.S. Pat. No. 6,432,820 to Lee et al., entitled Method of Selectively Depositing a Metal Layer in an Opening in a Dielectric Layer by Forming a Metal-Deposition-Prevention Layer Around the Opening of the Dielectric Layer, the content of which is incorporated herein by reference in its entirety.
FIG. 3 shows another type of defect that can result during deposition of conductive layers in high aspect ratio contact holes using HCM sputtering. A conductive layer 309 may be formed completely over the contact hole in an insulating layer 305 on an exposed impurity region 303 of a substrate 300, thereby forming the void 311. Accordingly, the types of defects shown in FIGS. 2 and 3 are variations of the same type of problem that can occur using conventional HCM sputtering.
FIG. 4 illustrates a contact hole 402 formed in a dielectric layer 405 on a substrate 400 that exposes a doped impurity region 403 therein. In particular, the contact hole 402 is formed in what was initially a stepped region 416 having a wider opening than the subsequently formed contact hole 402. The formation of the stepped region 416 may sometimes be formed as a measure to alleviate the problems shown above in FIGS. 2 and 3. However, use of the stepped region 416 can lead to a “shadowing” effect that can produce an overhang portion 415 in the contact hole 402 which can lead to the formation of a void in the conductive layer in the contact hole. In particular, as shown in FIG. 4, a sidewall portion of the contact hole 402 may be left exposed such that no portion of the conductive layer 409 is deposited thereon due to the overhanging portion 415.